1. Field of the Invention
The present invention relates to an angular velocity sensor for use in a car navigation system, a camera shaking prevention device, a robot attitude control device, and the like.
2. Description of the Related Art
A conventional angular velocity sensor 40 will be described below with reference to FIGS. 7 and 8. Four anchor portions 42 are formed at the four corners of a support substrate 41 made of Pyrex glass. L-shaped beams 43 are connected at one end to the anchor portions 42 and are connected at the other end to the four corners of a vibration weight 44, respectively. The vibration weight 44 serves as the load mass of the angular velocity sensor 40, and is allowed by the bending of the beams 43 to freely vibrate in the XY plane.
Comb-shaped movable electrodes 44a and 44b are formed on end faces (in the X-axis direction) of the vibration weight 44, and movable electrodes 44c and 44d shaped like the character are formed on the other end faces (in the Y-axis direction).
Fixed portions 45a to 45d are formed on the support substrate 41 between the adjoining anchor portions 42, respectively. A comb-shaped fixed electrode 46a formed on the inner side face of the fixed portion 45a is meshed with space therebetween with the movable electrode 44a to constitute a condenser 47a. A comb-shaped fixed electrode 46b formed on the inner side face of the fixed portion 45b is meshed with space therebetween with the movable electrode 44b to constitute a condenser 47b. Two F-shaped fixed electrodes 46c formed on the inner side face of the fixed portion 45c are meshed with space therebetween with the movable electrode 44c to constitute a condenser 47c. Furthermore, two F-shaped fixed electrodes 46d formed on the inner side face of the fixed portion 45d are meshed with space therebetween with the movable electrode 44d to constitute a condenser 47d.
A space 41a is formed under the beams 43, the vibration weight 44, the movable electrodes 44a to 44d, and the fixed electrodes 46a to 46d. In the angular velocity sensor 40, the elements, such as the anchor portions 42 and the vibration weight 44, excluding the support substrate 41, are formed by working a silicon substrate. The four anchor portions 42 and the fixed portions 45a to 45d, which are made of silicon, are joined onto the support substrate 41 of Pyrex glass by anode coupling.
Next, a description will be given of the operation of the angular velocity sensor 40. Since the angular velocity sensor 40 is operated with the anchor portions 42 connected to ground, the vibration weight 44 and the movable electrodes 44a to 44d are at ground potential.
The vibration weight 44 is vibrated by electrostatic attractive force in the X-axis direction by applying AC voltages having a phase difference of 180.degree., which are obtained by superimposing DC voltages, to the condenser 47a (between the anchor portion 42 and the fixed portion 45a) and the condenser 47b (between the anchor portion 42 and the fixed portion 45b). When the angular velocity sensor 40 rotates about the Z-axis passing through the center of the vibration weight 44 while the vibration weight 44 is thus vibrating, the vibration weight 44 receives a Coriolis force generated by the rotating force, and also vibrates in the Y-axis direction. The vibration components in the Yaxis direction are detected as capacitance changes by the condensers 47c and 47d, and these capacitance changes are converted into voltages and are differentially amplified, thereby determining the angular velocity.
In the conventional angular velocity sensor 40, the four anchor portions 42 made of a silicon material are joined to the four separate corners of the support substrate 41 made of a Pyrex glass material. The vibration weight 44 similarly made of a silicon material is supported integrally with the anchor portions 42 via the four beams 43.
Therefore, the difference in coefficient of thermal expansion between the support substrate 41 of Pyrex glass and the anchor portions 42 of silicon causes the joint portions therebetween to be warped. Because of this warp, the beams 43 connected to the vibration weight 44 receive compressive stress or tensile stress. The compressive stress and tensile stress become residual stress, which changes the vibration frequency of the vibration weight, and has an adverse effect on sensitivity of detection based on Coriolis force and the temperature characteristics of the mechanical resonant frequency of the vibration weight. For this reason, the detection sensitivity and the mechanical resonant frequency of the angular velocity sensor change substantially due to changes in temperature.